Let's get right to the surprise twist in the Oscar Pistorius trial. Pistorius expected to begin his testimony this morning, but the judge delaying the trial for more than a week. ABC's Matt Gutman is there in South Africa with the latest. Good morning, Matt. Reporter: Good morning, robin. That's right. We'll have to wait ten more days to hear Oscar Pistorius tell his version of events that night. Now, in this country it's customary for the defendant to take the stand first in his defense. Now, we expected that, what we didn't expect is for the judge's assistant to suddenly fall ill and for such a long postponement. It was supposed to be the day the blade runner walks into court and on to the witness stand. Instead, yet another delay. A surprise announcement from the judge. This matter will be postponed to the -- to Monday, the 7th of April. Reporter: The assessor is the judge's assistant who helps her pour through the mountain of evidence she is to analyze. Both sides concepted to that postponement. Earlier the prosecution rested turning the case over to the defense. Pistorius has admitted he shot his girlfriend, the model, reeva steenkamp in his bathroom last year but claims he mistook her for an intruder. On Tuesday, the defense asked for a two-day postponement. Following a day crammed with intimate details of Oscar and riva's relationship. 1700 messages most of them loving, the moment in the convenience store caught on camera. The kiss blowing selfie. I love it and it goes on so warm, thank you and it ends up with three crosses. Reporter: The love notes but the prosecution revealed a darker side of Pistorius angry and jealous texts to steenkamp. And I was standing tight behind you. Reporter: And her fear of him. I'm scared of you sometimes and how you snap at me and of how you will react to me. Reporter: Now, analysts tell us that Oscar Pistorius' testimony is that upon which the whole trial will hinge. What was his state of mind? Did he feel vulnerable and does that entitle him to shoot through a closed door at supposedly unknown targets whether it was steenkamp or an intruder? Josh. All right, Matt in Pretoria, South Africa. We will turn to chief legal affairs anchor Dan Abrams here for more on what would have been a big day in this trial. Oscar Pistorius' presumed testimony now delayed. How do you think, though, to this point they had an preparing? For days and months and you can imagine in his own head he has got to be going through every possible question he's going to be asked. Look, the key is trying to remain as consistent as possible with past statements that he's given. In the bail hearing he stated -- he gave a statement that said here's how it happened. Here's where I went. D there are going to be some issues that he's going to have to explain, for example, how did he go about getting his gun from underneath the bed and not realizing that she wasn't there? That will be a question that prosecutors are going to focus on so it's the sort of inconsistencies he's going to have to focus on and think about both in terms of his direct testimony and be prepared for in the cross-examination. Quickly, this is a man who seemed anything but disabled when running on the track but how do you think he might use his disability to his benefit in his testimony? Look, I think the defense is going to say that a reasonable person, remember, that's part of the standard. What would be a reasonable person do? The defense is going to say a reasonable person in his situation, a reasonable person who had his disability would be more vulnerable and, therefore, more afraid and they say that should give him more leeway in terms of what he did. So it's going to be an important question here. It's going to be an important issue and you can bet that prosecutors will try and turn it and say, you know, look at everything you've accomplished and say, you know, you didn't seem all that, you know, harmed by this for the rest of your life but I do expect that will be part of the defense. Remains to be seen. Today's delay a delay -- unbelievably how long it's delayed. They delay weeks on weeks. Into April. Thanks.

This transcript has been automatically generated and may not be 100% accurate.

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